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|Title: ||Morphological characterisation and evaluation of local cocoyam (Xanthosoma Sagittifolium [L] Schott) germplasm for disease resistance and other traits|
|Authors: ||Adofo, Kwadwo|
|Issue Date: ||22-Nov-2004|
|Series/Report no.: ||3646;|
|Abstract: ||A local collection of sixty-six (66) accessions of cocoyam from the Plant Genetic Resource Centre (PGRC), Bunso — Ghana was morphologically characterised and evaluated for disease resistance and other traits under field and Greenhouse/laboratory conditions.
The germplasm was morphologically characterised using the Descriptors for Xanthosoma from the International Plant Genetic Resource Institute (IPGRI, 1989) .
The evaluation for disease resistance or tolerance was done under two contrasting field environments (in terms of soil moisture regimes). The accessions were artificially inoculated with pathogens of the Cocoyam root rot blight complex diseases.
The properties of the accessions were also evaluated.
Results from the cluster analysis of the morphological data using SAS software (Ward’s Method), showed that the accessions could be grouped into two major clusters and five sub-clusters. The primary basis of the major clustering was the colour of the cormel flesh (red and White types). This indicated a narrow genetic diversity for the local cocoyam germplasn
Evaluation of the genotypes for disease resistance revealed the strong association between Susceptibility to diseases and moisture stress. The lowland environment characterized by high soil moisture, led to a severe attack from Dasheen mosaic virus, Bacterial leaf necrosis and concentric leaf spot diseases while Phytophthora leaf blight, Cladosporium leaf spot and Leptosphaerulina spot were mild. Cocoyam root rot blight complex disease was absent in this environment.
In the upland environment, insufficient soil moisture encountered predisposed the germplasm to the devastating attack of Phytophthora leaf blight, Cocoyam root rot blight complex and Bacterial leaf necrosis diseases and a mild attack from dasheen mosaic virus disease.
The Greenhouse and laboratory screening of the genotypes through artificial inoculation showed varied reactions and a similar trend as observed in the field. The field and Greenhouse screening thus revealed that most of the available germplasm are susceptible to the leaf blight and soft rot diseases. The white types appeared to be more tolerant than the red types.
The Physico-chemical properties investigated showed very little variation within the germplasm Sensory evaluation also indicated that 94% of the accessions had acceptable cooking quality.
It was concluded that the local cocoyam germplasm has a narrow genetic base and is highly susceptible to cocoyam root rot blight complex (soft rot) and Phytophihora leaf blight diseases especially when predisposed to moisture stress (deficit).
There is therefore the need to increase the existing variability by introducing germplasm from other cocoyam producing countries, or by embarking on hybridization, genetic transformations with biotechnological tools or the use of mutagenesis.|
|Description: ||A Thesis submitted to the School of Graduate Studies, Kwame
Nkrumah University of Science and Technology, Kumasi, in partial
fulfilment of the requirements for the Award of MSc. Agronomy (Plant Breeding option) degree, 2004|
|Appears in Collections:||College of Agric and Natural Resources|
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